Cutting tools of the kind in question are suitable for chip removing or cutting machining of workpieces of metal, such as steel, cast iron, aluminium, titanium, yellow metals, etc. The tools may also be used for the machining of composite materials of different types.
In practical production, the basic bodies and the replaceable cutting inserts for cutting tools are produced in two processes separated from each other and from materials having different properties. Usually, the basic body is manufactured from a solid steel body, in which the forming of the seat receiving the cutting insert is carried out by cutting machining, above all milling and drilling. By modern technique, this machining can be effected with very high accuracy in so far that the surfaces that delimit the seat and that ultimately determine the spatial position of the cutting insert, can be formed and located in a meticulously accurate way.
Also the cutting insert, which is a replaceable wear part, is traditionally given the form of a solid body of a homogeneous material that is considerably harder and more wear-resistant than the steel of the basic body. Most common in today's series manufactured cutting inserts is cemented carbide, which is a powder metallurgical material composed of one or more extremely hard carbides (e.g., WC, TiC, TaC and NbC) in a binder metal (usually Co). In a dry state, a powder mixture of selected components is compression-moulded while forming a green ware, which is later sintered while forming a usable cutting body (the dimensions of which all-around shrink approx. 18% in relation to the dimensions of the green ware). Similarly, the cutting inserts may also be manufactured from other materials than cemented carbide, e.g., cermet, ceramics, etc. It should also be mentioned that the finished cutting inserts may be coated as well as uncoated.
Within the field of cutting machining, there is a continuous development with the purpose of making not only the capacity of the tools to carry out the machining in a fast and accurate way more effective, but also the manufacture of the different parts of the tools in the form of basic bodies and replaceable cutting inserts. One trend is to improve the machining results in respect of the precision and surface finish, something which requires that the active cutting edge of the cutting insert obtains an exact, predetermined spatial position in relation to the rear fixing part of the basic body. In many applications, the requirements of positional precision are extreme. In today's cutting tools, generally a positional precision of the cutting edge is therefore aimed at which is counted in thousandths of a millimeter rather than in tenths. Another trend is to reduce the costs of the manufacture of the tools. This has, among other things, led to the fact that the cutting inserts manufactured from cemented carbide, which is most common on the market, already in connection with the compression-moulding or casting and sintering have received a better and better dimensional accuracy. To obtain good precision in the cutting inserts, it was earlier always necessary to subject the same to expensive grinding operations, but by the improved moulding and sintering technique, it has become possible to use directly pressed, i.e., unground cutting inserts to an ever greater extent. However, the development has not progressed further than that the tool designer still has to allow for a dimensional variation in the order of ±0.5% of the nominal dimensions of the cutting insert. This means that the active cutting edge of the cutting insert may very well end up in the desired position in the seat, when the outcome from the cutting insert production is good, but when the outcome is poorer (so far that the cutting insert has swollen and become longer, or shrunk and become shorter than intended), the position of the cutting edge in relation to the seat of the basic body may deviate to such a high extent from the desired position that the machining precision becomes less good.
In previously known cutting tools, the exact position of the active, front cutting edge was determined by the distance between the active cutting edge and two inactive clearance surfaces, positioned on the rear part of the cutting insert, which served as side contact surfaces and were pressed against a pair of co-operating, rear side support surfaces in the seat or insert seat of the basic body. When the rear clearance surfaces of the cutting insert form the reference point that determines the space position of the front, active cutting edge, the position precision of the cutting edge could become unacceptable if the cutting insert was not ground, because the distance between the active cutting edge and the opposite clearance surfaces could be considerable, in particular when the tools and the cutting inserts are large. In order to solve this problem, so-called serration connecting surfaces have—in particular for milling tools—been developed for holding the cutting inserts. Examples of such serration connecting surfaces in the interface between the cutting insert and the seat in the basic body are disclosed in, for example, WO2005/072898 and EP 1 795 288.
In certain tools, e.g., turning tools, serration connecting surfaces are, however, not suitable for different reasons, e.g., when it is desirable to make the turning inserts double-sided with the purpose of doubling the number of usable cutting edges. Another reason is that machining of a serration connecting surface in the seat of the basic body may be difficult and expensive to carry out, in particular when the turning inserts and thereby the seats are small.
A known turning tool is disclosed in U.S. Pat. No. 4,632,606. A theoretical merit with this tool is that the cutting body thereof does not require support via rear side contact surfaces against side support surfaces situated deep inside the seat of the basic body. Thus, the cutting body is, along two opposite long sides, formed with a pair of side contact surfaces, situated near an active cutting edge, which converge in the backward direction toward an intermediate part of the cutting body and are pressed against a pair of forwardly diverging side support surfaces in the seat. However, this merit is only theoretical so far that the location of the side contact surfaces situated far in the front or near the active cutting edge in no way guarantees an exact spatial location of the cutting edge in relation to the rear fixing part of the basic body. Thus, there are several sources of error between the rear fixing part of the basic body and the active, front cutting edge of the cutting body. A first source of error arises as a consequence of the fact that the seat for the cutting body is formed in a separate supplementary plate, which afterwards—via pins in co-operation with agglutination or welding—is fixed on top of a plane upperside of the basic body of the tool. Therefore, already in the basic body, a risk arises that the exact position of the seat—and thereby of the turning insert—in relation to the rear fixing part may go lost, namely if the tolerances of the pins and the holes of the basic body co-operating with the same become poor. In contrast to such countersunk seats that in modern cutting tools are formed by cutting or chip removing machining directly in the steel material of the basic body, the seat in the tool known by U.S. Pat. No. 4,632,606 runs in addition the risk of being dislodged from its initial position, if the turning insert during operation is subjected to great stresses. Another source of error may be that the proper cutting body is composed of a plurality of different parts, viz. a central carrier typically of steel and two inserts of a hard material, such as cemented carbide, ceramics or diamond, applied to the same by soldering or welding. This means that the two hard and chip-removing cutting inserts individually may obtain an erroneous (and differing) position in relation to the central carrier already in connection with the manufacture of the cutting body. Because the carrier of the cutting body and the two separate inserts are formed of different materials, which may have different coefficients of thermal expansion, the risk of another source of error furthermore arises. For example, the material in the carrier, e.g., steel, has a greater coefficient of thermal expansion than the material in the inserts. When heat is generated during the cutting process, then the material in the carrier will be expanded and displace the cutting edge of the individual insert in relation to the side contact surfaces being behind, more precisely in such a way that the distance between the cutting edge and the side contact surfaces is enlarged.
The present invention aims at managing problems of the type that may arise in such modern cutting tools that make use of unground cutting inserts of above all cemented carbide, more precisely by providing a cutting tool the cutting inserts of which should be possible to manufacture by direct pressing, without needing any complicating and price rising connecting surfaces to give the cutting edges a good, repeatable position precision. In other words, it should be possible to fix the cutting insert in a reliable way and support the same along side contact surfaces thereof, without possible form defects during the manufacture jeopardizing the position precision of the cutting edges.
Another object of the invention is to provide a cutting tool, the cutting inserts of which are double-sided and thereby afford the user a great (doubled) number of cutting edges. Furthermore, the cutting inserts of the tool should, in spite of the indexability thereof, always be possible to be retained in a reliable and stable way in the appurtenant seat in the basic body of the tool, among other things in so far that each tendency of the cutting insert to rise (i.e., partially lose the contact with the bottom of the seat) is efficiently counteracted. Neither should the cutting insert be able to turn in the seat.
An additional object is to provide a cutting tool, the means of which for the fixation of the cutting insert should be possible to embody in various ways to fit different applications. Thus, the fixation means should be selectable among: screws, clamps, levers and wedges. Furthermore, it should be possible to carry out the manufacture of the basic body as well as the replaceable cutting inserts in series in an expedient way in order to reduce the tool costs to a minimum. In other words, the basic body and the cutting insert should individually be producible from solid bodies in a single piece without the need of price rising finishing.